The former Paymaster General, who was forced to quit after his financial relationship with Mr Mandelson, then Trade and Industry Secretary, came to light, said the version of events his former friend presented to MPs was "not true".

The Tories seized on the allegations and said that Mr Mandelson, now Northern Ireland Secretary, would have to resign from the Cabinet if the claims published in Mr Robinson's memoirs proved to be right. David Heathcoat-Amory, the shadow trade secretary, said he had written to Robert Sheldon, the chairman of the Commons standards and privileges committee, to ask for a new inquiry into the £373,000 home loan.

He acted before publication of Mr Robinson's memoirs, which challenge the truth of the account Mr Mandelson gave to the standards committee in May last year after Elizabeth Filkin, the parliamentary commissioner for standards, ruled that he had breached the MPs' code of conduct.

At odds between the two men, now bitter enemies, is the conversation they had at a private dinner on May 23, 1996, a year before Labour came to power, when they discussed Mr Mandelson's desire to buy a house in Notting Hill, west London.

Mr Mandelson maintains that he did not go to the dinner with the intention of asking Mr Robinson, a close ally of Gordon Brown, for money. According to his evidence to MPs, Mr Robinson offered him "help" with the cost of the house purchase.

Last night Mr Robinson told the Daily Mail, which published the first of a series of extracts from his book, that he rejected Mr Mandelson's account as "not accurate - I can say that categorically. He is saying I talked him into taking the money. That is not true."

In the book he says: "He was looking for a loan. He initiated the discussion of his financial circumstances and of his flat. He told me how miserable he felt there. What I heard from Peter was a cri de coeur."

Mr Mandelson did not tell Tony Blair, then leader of the Opposition, that he had borrowed a significant sum from Mr Robinson, who had close links with the late Robert Maxwell. Nor did he mention it to the building society which held his mortgage. The discovery of the loan, on the eve of Christmas 1998, plunged the Government into crisis.

Mr Mandelson spent 10 months on the backbenches before being bought back into the Government by Mr Blair as Northern Ireland Secretary. Although Mrs Filkin criticised his handling of the loan, the standards committee concluded that he had "acted without any dishonest intention" and ruled out further action.

The book discloses the extent of Mr Robinson's anger at the way he was treated by Mr Mandelson and Mr Blair over the affair. Although the difference between the two is one of interpretation, the fact that Mr Robinson has chosen to make public his side of one of the most damaging scandals of the Blair administration set alarm bells ringing in Downing Street.

A Downing Street spokesman tried to dismiss the story as of no consequence. He said: "The way we view this is a rehash of something that was settled two years ago in order to help sell books. These things were looked into at the time and a ruling was made - that's that."

David Blunkett, the Education Secretary, joined a concerted effort sanctioned by Downing Street to discredit Mr Robinson. He accused him of being "self-indulgent" and of damaging Labour's interests. John Reid, the Scottish Secretary, dismissed the claims as "old froth".

Mr Mandelson reiterated his version of the dinner. He said: "During the course of the evening I mentioned to [Mr Robinson] that I was trying to find somewhere to live in London. We talked about house buying and how expensive it was. Geoffrey said: 'If you are stuck for cash and need financial help, don't hesitate to ask.'"

Although Mr Robinson does not say explicitly that Mr Mandelson initiated the subject of a loan, he makes clear that he believed his colleague was prompting him to make an offer. His account describes how he believed that Mr Mandelson needed a suitable residence where, as Trade Secretary, he could entertain guests.

"I asked what he had in mind. He replied: 'Oh, a place in Notting Hill is what I would really like. But it is too expensive and there is no one to help me.' At this point I said that I might be able to assist if he wanted me to."